linux-kernel - Re: [PATCH] erofs: fix missing xas

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Date:   Mon, 14 Nov 2022 12:42:29 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Jingbo Xu <jefflexu@...ux.alibaba.com>
Cc:     xiang@...nel.org, chao@...nel.org, yinxin.x@...edance.com,
        linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        dhowells@...hat.com
Subject: Re: [PATCH] erofs: fix missing xas_retry() in fscache mode

On Fri, Nov 11, 2022 at 05:08:13PM +0800, Jingbo Xu wrote:
> The xarray iteration only holds RCU and thus may encounter
> XA_RETRY_ENTRY if there's process modifying the xarray concurrently.
> This will cause oops when referring to the invalid entry.
> 
> Fix this by adding the missing xas_retry(), which will make the
> iteration wind back to the root node if XA_RETRY_ENTRY is encountered.
> 
> Fixes: d435d53228dd ("erofs: change to use asynchronous io for fscache readpage/readahead")
> Signed-off-by: Jingbo Xu <jefflexu@...ux.alibaba.com>

Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>

Thanks,
Gao Xiang

> ---
>  fs/erofs/fscache.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index fe05bc51f9f2..458c1c70ef30 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -75,11 +75,15 @@ static void erofs_fscache_rreq_unlock_folios(struct netfs_io_request *rreq)
>  
>  	rcu_read_lock();
>  	xas_for_each(&xas, folio, last_page) {
> -		unsigned int pgpos =
> -			(folio_index(folio) - start_page) * PAGE_SIZE;
> -		unsigned int pgend = pgpos + folio_size(folio);
> +		unsigned int pgpos, pgend;
>  		bool pg_failed = false;
>  
> +		if (xas_retry(&xas, folio))
> +			continue;
> +
> +		pgpos = (folio_index(folio) - start_page) * PAGE_SIZE;
> +		pgend = pgpos + folio_size(folio);
> +
>  		for (;;) {
>  			if (!subreq) {
>  				pg_failed = true;
> -- 
> 2.19.1.6.gb485710b